Generally, the basic steps of processing color photographic materials comprise a color developing step and a desilvering step. In the color developing step, imagewise exposed silver halide is reduced with a color developing agent to produce silver, and the oxidized color developing agent reacts with color forming couplers to form dye images. In the following desilvering step, the silver produced in the color developing step is oxidized by the action of an oxidizing agent (the so-called bleaching agent) and is then dissolved by a complexing agent (the so-called fixing agent) of a silver ion. Through this desilvering step, only dye images are formed in the thus-processed color photographic material.
To carry out the above desilvering step, there are two basic methods generally employed: (1) using two baths, that is, a bleaching bath containing a bleaching agent and a fixing bath containing a fixing agent; (2) using one bath, that is, a bleach-fixing bath containing a bleaching agent and a fixing agent together.
In practice, in addition to the above basic types of desilvering steps, a developing process normally includes various auxiliary steps for retaining the photographic and physical qualities of the image or for improving the quality of the image during storage. For example, such practical developing processes further include a hardening bath, a stop bath, an image stabilizing bath and a washing bath.
Bleaching agents are generally known, and include, for example, red prussiate, dichromates, ferric chloride, aminopolycarboxylic acid ferric complex salts and persulfates.
However, red prussiate and dichromates generally cause environmental problems due to the need to dispose of cyanides and hexavalent chromium compounds, and their use requires special processing facilities. If ferric chloride is used, there are, in practice, various obstacles to be overcome in view of problems such as the formation of iron hydroxide in the subsequent washing step, as well as the occurrence of stain. Persulfates are very weak in their bleaching ability, and thus disadvantageously require very prolonged bleaching time. Further, although methods additionally employing a bleaching accelerator are suggested, since persulfates are designated as dangerous articles, various measures must be taken to store them. Therefore, they are disadvantageously problematic for practical usage.
Aminopolycarboxylic acid ferric complex salts (particularly, ethylenediaminetetraacetic acid ferric complex salt) are accompanied by few environmental problems. Thus, they are currently most widely used. However, the bleaching power of aminopolycarboxylic acid ferric complex salts could withstand some improvement, and when a silver halide color photographic material composed mainly of a silver chlorobromide emulsion having a relatively low sensitivity is subjected to bleaching or bleach-fixing by using this type of bleaching agent, sufficient desilvering can be attained. However, when a color photographic material composed mainly of a bromochloroiodide emulsion or a bromoiodide emulsion which is color-sensitized and has a relatively high sensitivity (in particular, a color reversal photographic material for films using an emulsion having a high quantity of silver, or a color negative photographic material for films) is processed using this type of bleaching agent, it is disadvantageous in that insufficient desilvering occurs, or bleaching takes a longer period of time. For example, when a color negative photographic material for films is bleached using a bleaching solution containing an aminopolycarboxylic acid ferric complex salt, a bleaching period of at least 4 minutes is required, and to retain sufficient bleaching power, a complicated method including controlling the pH of the bleaching solution and aerating the solution, is required. Even when such a complicated method is used in practice, however, insufficient bleaching occurs often.
Further, after the bleaching process, to fully effect desilvering, the photographic material should be processed with a fixing solution for at least 3 minutes. Thus, it is eagerly desired to shorten the processing time for this type of desilvering process.
On the other hand, as a measure to reduce the time required for the desilvering step, it is known to use a bleach-fixing solution containing both an aminopolycarboxylic acid ferric complex salt and a thiosulfate as described in German Pat. No. 866,605, but when an aminopolycarboxylic acid ferric complex salt that has a weak oxidizing power (bleaching power) itself is co-present with a thiosulfate having a reducing power, the bleaching power becomes very weak, so that it is quite difficult to sufficiently desilver a color photographic material for films high in sensitivity and silver content, and this method is also impractical. Of course, to overcome the disadvantages of such a bleach-fixing solution, various attempts have been made. For example, such attempts include the methods described in British Pat. No. 926,569 and Japanese Patent Publication No. 11854/78 wherein an iodide or a bromide is added to the solution, and the method described in Japanese Patent Application (OPI) No. 95834/73 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") wherein triethanolamine is used to allow a highly concentrated aminopolycarboxylic acid ferric complex salt to be contained in the bleach-fixing solution, but the effects of such attempts are not satisfactory to attain the desired practical results.
In addition to insufficient desilvering ability, bleach-fixing solutions also are problematic in that cyan dyes formed by color development may be reduced to leuco dyes, thus adversely affecting color reproduction. To overcome this defect, for example, U.S. Pat. No. 3,773,510 suggests increasing the pH of a bleach-fixing solution. However, increasing the pH of a bleach-fixing solution results in a further decrease in the bleaching power, which is unacceptable from a practical viewpoint. Further, in U.S. Pat. No. 3,189,452, a method is disclosed wherein after bleach-fixing, leuco dyes can be oxidized with a red prussiate solution to reconvert them to cyan dyes, but the use of red prussiate is accompanied by the environmental problems as mentioned above, and if bleaching is carried out after the bleach-fixing, there is little effect seen as to decreasing the amount of remaining silver.
Further, with a view toward preventing environmental pollution, it is required to recover and treat photographic processing liquids that are high in biochemical oxygen demand (BOD) and chemical oxygen demand (COD), and the development of a method of processing color photographic materials wherein the amount of waste liquor is reduced contributes to lowering the recovery and treatment costs of the waste liquors, and thus is keenly desired.